package Code;

import java.util.List;

public class Code141 {
    // 定义链表节点类
    static class ListNode {
        int val;
        ListNode next;
        ListNode(int x) {
            val = x;
            next = null;
        }
    }
    static boolean hasCycle(ListNode head) {
        if(head == null|| head.next == null){
            return false;
        }
        ListNode slow = head;
        ListNode fast = head.next;
        while(slow != fast){
            if(fast == null || fast.next == null){
                return false;
            }
            slow = slow.next;
            fast= fast.next.next;

        }
        return true;
    }
    public static void main(String[] args) {
        ListNode head = new ListNode(1);
        ListNode node2 = new ListNode(2);
        ListNode node3 = new ListNode(3);
        ListNode node4 = new ListNode(4);
        head.next = node2;
        node2.next = node3;
        node3.next = node4;
        node4.next = node2; // 创建环


        boolean result = hasCycle(head);
        System.out.println("链表中是否有环: " + result);
    }
}
